Method of making metal-plated plastic articles

ABSTRACT

A platable plastic component and a nonplatable plastic component are joined together into a multicomponent article. The entire multicomponent article is then processed in an operation for plating plastics having the steps of introducing the multicomponent article into a strong oxidizing acid solution, followed by introducing the article into a noble metal solution, then introducing the article into an electroless nickel or copper bath, and finally further processing the article in conventional plating baths.

United States Patent Hepfer 5] Feb. 8, 1972 [54] METHOD OF MAKINGMETAL-PLATED PLASTIC ARTICLES [72] Inventor: Ivan C. Hepfer, Caledonia,Mich.

[731 Assignee: Furniture City Manufacturing Corp.,

Grand Rapids, Mich.

- [22] Filed: Apr. 1, 1969-- 211 App]. No.1 811,706

Y 156/280, 161/182 51 1 161. C1. ..C23b 5/02 [58] new 61 Search..156/244, 91, 92, 150, 280

[56] References Cited UNITED STATES PATENTS 3,416,992 12/1968 Amos156/150 x 3,420,679 1/l969 01116111 et a1... 3,433,688. 3/1969 Staats et61.... 3,444,0l8 5/1969 Hewitt ..156/92 x 3,453,173 7/1969 lsley et al...156/244 x 3,475,248 10/1969 Brasure... ..156/244 x 3,477,126 11/1969Price ..156/244 x 3,476,627 11/1969 Squires ..156/244 3,486,196 12/1969Kcenk et al ..156/244 x 3,562,038 2/1971 Shipley et al ..156/150 xPrimary Examiner-Harold Ansher Azt0rneyPrice, Heneveld, Huizenga &Cooper ABSTRACT A platable plastic component and a nonplatable plastic'component are joined together into a multicomponent article. The entiremulticomponent article is then processed in an operation for platingplastics having the steps of introducing the multicomponent article intoa strong oxidizing acid solution, followed by introducing the articleinto a noble metal solution, then introducing the article into anelectroless nickel or copper bath, and finally further processing thearticle in conventional plating baths.

9 Claims, 6 Drawing Figures METHOD OF MAKING METAL-PLATED PLASTICARTICLES BACKGROUND This invention relates to the structure of plasticarticles and to the plating of metal onto the surface of plasticarticles. In many instances, a manufacturer may desire a plasticarticlewhich is plated with a protective or decorative coating on only aselected area or portion of the article. The reasons for a choice ofthis nature are many and varied. For example, one might desire thehighly decorative effect which can be achieved by contrasting a platedsurface with an exposed unplated surface. Alternatively, it is oftennecessary to have an article which is selectively conductive to heat orelectricity through plating which is on only certain portions of itssurface. Still another motive for such an article is the fact thatstructural parts thereof may be required solely for strength and shouldnot be plated to avoid unnecessary costs.

There are many difficulties in the selective plating of a unitaryplastic article. For example, the use of selective masking and theapplication of resists (stopoff lacquers) that do not become platedduring the normal plating operation are in general extremely critical,difficult and expensive to apply. Further, such techniques often produceinconsistent results, and they also involve the need for workers who aretechnically skilled beyond the usual calling. One way to avoid thisbasic underlying problem might be to provide separate component parts ofan article, completely plate those components having surface portionswhich are desired to be plated, and then assemble the componentstogether to form the finished article, such that only the desiredportions of the plated components are exposed. This approach has severalapparent limitations. Firstly, considerable plating metal and expense iswasted. Furthermore, if the unplated plastic components are molded ontothe plated components, the high heat of the second molding operation cancause cracking and peeling of the plating on the already-platedcomponent. Additionally, critically close tolerances in the plating ofthe first component will be required in order for it to properly fit themold into which it must be placed when molding the second component ontothe first. Other means of attachment besides molding, such assonicwelding, adhesive bonding, heat staking and hot stamping, alsorequire close control of the plating thickness.

SUMMARY are made passe. Molding and plating techniques can beliberalized since the plated part is not exposed to high tem- *peraturenor is the second molding operation affected by the plate thickness.Finally, the waste of plating on unexposed surfaces is eliminated.

The nature of the article produced in this process can be discerned byreference to the written disclosure and appended drawings wherein:

FIG. I is a side view of a bicomponent toggle switch embodying theinvention;

FIG. 2 is a cross section of the toggle switch taken along line llllofFIG. 1;

FIG. 3 is an enlarged, fragmentary sectional elevation show- 1 ing theintersection of a platable plastic component and a nonplatable plasticcomponent;

FIG. 4 is an overhead plan view of a circuit board embodying theinvention;

FIG. Sis an enlarged, fragmentary sectional elevation taken on line V-Vof FIG. 4; and

FIG. 6 is a fragmentary perspective view of a platable plastic componentin another embodiment of the invention.

PREFERRED EMBODIMENT Some plastic materials, notably ABS(acrylonitrile-butadiene styrene copolymer) are readily plated withmetallic coatings such as copper, nickel and chromium. Such coatings areapplied for decorative effects or for functional purposes, such asconductivity, wear resistance, etc. The usual plating process oroperation for plastic includes the basic steps of chemically etching orconditioning the surface of the plastic, usually in a strong oxidizingacid solution; activating the conditioned surface in a noble metalsolution; applying an initial metallic coating to the plastic in anelectroless nickel or copper bath; and then further plating the plasticwith a desired metal in conventional electroplating solutions. It ispresently thought. that the first step in this plastic plating processetches or conditions the surface of the plastic such that the noblemetal solution of the next step will then wet the surface of the plasticand be adsorbed thereon. Furthermore, the noble metal salt which isadsorbed is reduced, by the use of various techniques, resulting in anadsorbed noble metal such as palladium on the surface. The surface isthen said to be activated so that the electroless solution used in thethird step will deposit a thin initial metallic coating upon whichheavier electrodeposits can be applied. The fourth step then conforms toconventional electroplating procedures.

On the other hand, some plastics are not as readily platable as ABS. ABSis a terpolymer, including styrene, butadiene and acrylonitrile. Becausebutadiene is a double bond polymer, it is active and vulnerable tochemical attack and hence the ABS becomes etched in the conditioningbath. Plastics such as polypropylene, however, do not generally includesuch chemically vulnerable components and hence are not platable inprocesses by which ABS is readily platable. They are not conditioned, donot wet, and consequently are neither activated in the noble metalsolution nor plated in the electroless plating solution or theelectroplating procedures. Polypropylene is a single bond monopolymerand as such is quite stable. Other examples of plastics which are notplatable in a process which will readily plate ABS include thefollowing: polysulfone, polyphenylene oxide, polycarbonate, rigidpolyvinyl chloride, and diallyl phthalate.

Some of the aforementioned plastics which are not readily platablecan'in fact be plated by altering the basic process by which ABS isplated. For example, a preconditioning solvent etch can be employed, thesolution of strong oxidizing acid or other etching solution can be mademore concentrated, and the temperature thereof can be elevated. Otherpossible alterations of the basic process which may be useful in somecases include introducing the plastic into an accelerating bath prior toits introduction into the noble metal solution; and introducing it intoa post-nucleating bath following the noble metal solution treatment.

Thus, the basic electroless process can be altered such that a plasticwhich is not readily platable, such as polypropylene, can in fact beplated. There are, however, plastics which are particularly chemicallyresistant, and which are not platable even under the altered basicprocess referred to above. Under these circumstances, however, far fewerplastics are unplatable and the versatility of the method becomes morelimited. In addition, the operating conditions of the electrolessprocess become considerably more critical than they are when thecomponent to be plated is ABS.

Finally, it should be mentioned that considerable work is being done toalter the composition of the plastics such as polypropylene oxide,polysulfone, and other so-called nonplatable plastics, such that theywill be platable in a process which will plate ABS. One approach to thisinvolves the introduction of butadiene into the molecular structure.Such modified plastics which have properties such that they can beplated by a process used for plating ABS and can be used in place of ABSin this invention, where another component is used which is not platedduring the process.

The present invention capitalizes on the fact that certain types ofplastic are platable by a given process while other types of plastic arenot platable by the same process. In any given application of theinvention, the first such plastic can be referred to as a platable"plastic, while the second can be referred to as a nonplatable plastic,and these terms are to be interpreted in this relative manner in thisspecification, rather than in an absolute sense. According to theinvention, a nonplatableplastic component is joined with a platable"plastic component; and the entire resulting multicomponent article isprocessed in a plastic plating process of the nature described above,such that the exposed portions of the platable plastic component acquirea metal surface while the exposed portions of the nonplatable plasticcomponent remain unplated. In some instances, the platable component maycover the entire surface of a nonplatable substrate. The lattercomponent is selected because of its strength or other desirableproperties while the former component is selected in order to lendbeauty to the article.

One example of this invention is a toggle switch as shown in FIGS. 1 and2. Basically, this is a conventional switch and operates by thewell-known toggle snap action. It has a lever component 14 joined to aworking component having a working'surface 11, with the lever component14 having a plated surface 16. The working component 15 of toggle switch10 must be made of a plastic which is relatively hard, has goodstrength, has good wear resistance, and has good heat and electricalresistance. Plastics such as polypropylene, polysulfone, polyphenyleneoxide, phenolics and certain glass-filled materials meet thesestandards. Since working surface 11 of toggle switch 10 must also befree of all metal in order to avoid electrical shorts, working component15 of the switch must additionally be an unplated plastic material. Theabove-named plastics have a non-platable" quality when the levercomponent 14 of the switch 10, which should have a decorative surfaceand hence be a plated plastic, is ABS. In this case, a polycarbonate isvery suitable for the nonplatable or working component 15.

In producing toggle switch 10, the higher melting point plastic ismolded first. Usually this will be the nonplatable plastic component 15as is the case where a polycarbonate is used for this component and ABSis used for the platable plastic component or lever component 14. Thelower melting point plastic component may then be molded directly ontothe higher melting point plastic component. In the advent a thermosetmaterial is used as one component, it must be molded first because ofthe temperatures and pressures involved. This order is necessary, lestthefirst molded component be warped when the second component is moldedto it. The dies used in molding these components are designed to produceinterlocking means 13 for holding the two components 14 and 15 together;for example, hollow passages or voids may be formed in components 15which are filled by the plastic of which component 14 is made when thelatter is molded upon component 15.

The molding and joining of the two components for the switch 10 can beaccomplished with two molds, i.e., a first mold for molding thecomponent 15 and the second mold for receiving the molded component 15andmolding the second component 14 onto it. This would be necessary inthe event that one component is a thermoset and the other athermoplastic material. Where the components are to be made of plasticshaving comparable thermal characteristics, there are other ways to jointhem, such as by using a single index mold having dual gating in amachine with dual injection systems. The indexing of the mold can beaccomplished either by indexing the platen of the machine to which themold is attached, or by constructing the mold so that it will indexitself as it is opened. A third alternative is to mold the components 14and 15 in completely separate operations and then join them, as by anappropriate adhesive or by a desired mechanical means. Some commonmechanical means of joining the two components are sonic welding, spinwelding, heat staking and various fasteners. Hot stamping may also beemployed where a thermoplastic film is to be joined to another film ormolded plastic component.

Once the lever, or platable plastic component 14, and the working ornonplatable plastic component 15 are joined, the resultingmulticomponent structure is processed in the plastic plating process. Itis introduced into a chemical conditioning solution of a strongoxidizing acid; then it is introduced into an activating or noble metalsolution; then it is introduced into an electroless plating solution,generally of copper or nickel; and finally it is electroplated inconventional electroplating baths. ln-the first step of the platingoperation, the ABS or other platable component 14 is chemically etchedor conditioned, whereas the polycarbonate component 15 is not chemicallyattacked by the strong oxidizing acid and remains in its smooth, asmolded" condition. In the second step, the condition ABS component 14absorbs the noble metal salt on its surface and becomes activated,"while the polycarbonate component 15 does not wet" and thus does notabsorb the noble metal salt. In the third step, the ABS component 14 inits activated form takes on a thin layer of metal by chemical reductionof the electroless plating solution. The unactivated polycarbonatecomponent 15, however, remains unaffected by the electroless platingsolution. The fourth step of further processing the article inconventional plating baths builds heavier metallic deposits on the ABScomponent 14, but does not affect the polycarbonate component 15. Theresulting surface plating 16 on the ABS component 14 is well bonded tothis component, having peel-pull strengths of 5 and 10 pounds or morewhen a 1 inch strip of plating is pulled at from the surface of theplatable component 14. Thus, the end result of this process is a veryattractive and very useful unitary article having certain predeterminedportions fully plated and other portions completely unplated, asdesired.

The process of plating a previously assembled multicomponent article isnot without its difiiculties, however. The electroplating process, thefourth step in the plastic plating process, has the tendency to depositrough protrusions or projections on sharp edges, referred to in the artas treeing." This treeing effect is also exhibited at the intersectionof the exposed surfaces of the platable and nonplatable plasticmaterials, but it can be diminished, if not eliminated, by designing themulticomponent article such that the intersections of the exposedsurfaces of the platable and nonplatable plastic components defineshielding configurations. For example, it will be noted that theintersections of the exposed surfaces of the platable plastic component14 and the nonplatable plastic component 15 of the toggle switch 10define inside corners 17. Such inside comers shield the points ofintersection of the exposed surfaces and lower the current density atthese points; consequently, the presence of a nonplatable wall adjacenta platable wall and at roughly right angles thereto will act to shieldthe platable wall and prevent treeing.

FIG. 3 shown another example of this invention for the purpose ofillustrating another type of shielding configuration. As an alternativeto inside corners l7, grooves 52 can be designed at the intersection ofthe exposed surfaces of platable and nonplatable components. Moreparticularly, where a platable plastic component 20 is joined to anonplatable plastic component 30 in an exposed plane, where the exposedintersecting surfaces of the platable plastic material 20 and thenonplatable plastic material 30 would normally form a continuous planarsurface, it is advantageous to provide a groove 52 along suchintersection. were it not for such a groove, the treeing phenomenonwould occur at the line of intersection of the two plastic components.The presence of the groove 52 lowers the current density at theintersection of the surfaces, and thus will prevent, or at leastsubstantially reduce, the treeing effect. The groove 52 should be quitedeep and relatively steep, so that the current density in the groove 52will be appreciably lower than that at the shoulder 53 of the groove 52.The steep throw in the groove 52 tends to feather out the plated coating40 as it extends into the groove 52. Thus, in the groove type ofshielding configuration 52 as well as the inside corner type ofshielding configuration 51, the presence of the adjacent nonplatablewall at generally right angles of the platable wall acts to shield theplatable wall and thus prevent treeing." Another advantage of this typeof design is that the edge of the plate is protected from catching" andbeing torn loose when the surface on the article is abraded at theintersection of the plated and unplated surface. An additional advantageis that any "treeing that does occur is not as obvious as it would be ifthe groove design were not used.

Another example of this invention is the printed circuit board 60 ofP168. 4 and 5. In this embodiment, panel board 64 is made of anonconductive nonplatable plastic material. If made of a polycarbonate,it will be molded first with appropriate openings for the circuitrypattern 63, which is then molded onto the circuit board 64 out of aplatable plastic material such as ABS. As can be seen from the crosssection in FIG. 5, the circuit pattern or platable plastic component hasinterlocking edge means 62 which are molded into recesses molded intothe circuit board 64. There are openings 61 in the board for mountingelectrical components, and these openings are also formed in theplatable plastic circuit path portions 63. Also, it should be noted thatthe intersection of the exposed surface of the platable plasticcomponent 63 with the exposed surfaces of the nonplatable plasticcircuit board 64 have been designed to define grooves 66, which aredirectly analogous to the groove 52 described above, and which provide ashielding configuration such as was discussed in the previous example.Shoulder 67 is analogous to shoulder 53 above. The actual molding andjoining operations for the circuit board 60 can be performed in any ofthe ways which were described in connection with the toggle switch 10.After the platable plastic circuitry pattern 63 is joined to thenonplatable circuit board 64, the entire circuit board assembly 60 isthen processed through conditioning, activating, electroless plating andelectroplating solutions as described previously. The platable plasticcomponent 63 becomes plated with a metal coating 68, as shown in thecross section of FIG. 5, and the nonplatable plastic component 64 is notplated at all. The circuitry pattern 63 will then conduct electricity,while the circuit board 64 will not. For purposes of electroplating, theentire circuitry patten 63 should be interconnected as shown in FIG. 5,and these interconnections may be ground off or stripped off wherenecessary once the circuit was completely plated. Thus, it is possibleto produce printed circuit boards 60 without resorting to thephotographic methods or strip back methods which are commonly usedtoday.

Finally, the device of FIG. 6 is also made of a platable plasticcomponent 70 and a nonplatable plastic component 80. The purpose of thisexample is to demonstrate still another way of joining a platableplastic component to a nonplatable plastic component. Because of theuniform configuration of the device of this example along itslongitudinal axis, it can be manufactured by extruding the two differentplastic materials from a dual extrusion die. Thereafter, the platingprocess is the normal plastic plating operation as previously described.

It is understood that the above description of this invention is merelythe preferred embodiment with examples, and that changes, alterations,and other applications could be made thereof without departing from thespirit and broader aspects of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A method of making an article of manufacture of a predetermined shapein which certain predetermined exposed areas are to be metallic platedand the remaining exposed areas are not comprising the following stepsin the order recited: selecting an electroless preplating process forapplying an initial metallic coating to a plastic; joining a firstplastic component, which is platable by said electroless platingprocess, with a second plastic component which is not platable by saidelectroless plating process, in a manner covering portions of thesurface of said first plastic component and leaving predeterminedexposed areas to be metallic plated and said second plastic componenthas exposed surfaces corresponding to the said remaining exposed areaswhich are not to be plated, and thereby selectively masking portions ofthe surface of said first platable plastic component; processing thejoined multicomponent article by said electroless plating process tothereby deposit an initial metallic coating on the exposed surfaces ofsaid platable plastic component; finally processing said joinedmulticomponent article in electrolytic plating baths to thereby furtherplate said exposed surfaces of said platable plastic component.

2. The method of claim 1 wherein said step of joining said componentsincludes the orienting of the said exposed surfaces of one suchcomponent at an angle to the exposed surfaces of the other at theintersection of said exposed surfaces, to provide a shieldingconfiguration at such intersection for diminishing the treeing effect ofthe plating there.

3. The method of claim 1 wherein said joining step is carried out bymolding one of said plastic components over the other such component.

4. The method of claim 3, wherein said one component is said firstplatable component.

5. The method of claim 1, wherein said joining step is carried out bymechanically fastening said components together.

6. The method of claim 1 wherein said joining step is carried out byextruding one of said components onto the other.

7. The method of claim 11, wherein said components are extruded togetherin interconnected relation. 8. A method of making an article ofmanufacture of a predetermined shape in which certain predeterminedexposed areas are to be metallic plated and the remaining exposed areasare not comprising the following steps in the order recited: selecting aconditioning bath for use in an electroless preplating process; joininga first plastic component, which is vulnerable to chemical attack insaid conditioning bath, with a second plastic component which is notvulnerable to chemical attack in said conditioning bath, said firstplastic component having exposed surfaces corresponding to the saidcertain predetermined exposed areas to be metallic plated and saidsecond plastic component having exposed surfaces corresponding to thesaid remaining exposed areas which are not to be plated, the said firstand second components being joined in a manner covering portions of thesurface of said first component and leaving other portions exposed thusselectively masking the unexposed surface of said first plasticcomponent; processing the joined multicomponent article in saidconditioning bath to thereby condition the exposed surfaces of saidfirst plastic component; activating said conditioned surface of saidfirst plastic component; applying an initial metallic coating to saidactivated surface in an electroless bath; finally processing saidjoined; multicomponent article in an electrolytic plating bath tothereby plate said exposed surfaces of said first component.

9. A method of making an article of manufacture comprising the followingsteps in the order recited; joining a first plastic component consistingof an acrylonitrile butadiene styrene copolymer with a second plasticcomponent selected from the group consisting of polypropylene, apolysulfone, polyphenylene oxide, a polycarbonate, rigid polyvinylchloride and diallyl phthalate in a manner covering portions of thesurface of said first plastic component and leaving other portionsexposed thus selectively masking the surface of said first component;processing the joined multicomponent article in electroless platingbaths to thereby deposit an initial metallic coating on to the exposedsurfaces of said first plastic component; finally processing said joinedmulticomponent article in an electrolytic plating bath to therebyfurther plate said exposed metallic coated surface of said first plasticcomponent.

2. The method of claim 1 wherein said step of joining said componentsincludes the orienting of the said exposed surfaces of one suchcomponent at an angle to the exposed surfaces of the other at theintersection of said exposed surfaces, to provide a shieldingconfiguration at such intersection for diminishing the treeing effect ofthe plating there.
 3. The method of claim 1 wherein said joining step iscarried out by molding one of said plastic components over the othersuch component.
 4. The method of claim 3, wherein said one component issaid first platable component.
 5. The method of claim 1, wherein saidjoining step is carried out by mechanically fastening said componentstogether.
 6. The method of claim 1 wherein said joining step is carriedout by extruding one of said components onto the other.
 7. The method ofclaim 11, wherein said components are extruded together ininterconnected relation.
 8. A method of making an article of manufactureof a predetermined shape in which certain predetermined exposed areasare to be metallic plated and the remaining exposed areas are notcomprising the following steps in the order recited: selecting aconditioning bath for use in an electroless preplating process; joininga first plastic component, which is vulnerable to chemical attack insaid conditioning bath, with a second plastic component which is notvulnerable to chemical attack in said conditioning bath, said firstplastic component having exposed surfaces corresponding to the saidcertain predetermined exposed areas to be metallic plated and saidsecond plastic component having exposed surfaces corresponding to thesaid remaining exposed areas which are not to be plated, the said firstand second components being joined in a manner covering portions of thesurface of said first component and leaving other portions exposed thusselectively masking the unexposed surface of said first plasticcomponent; processing the joined multicomponent article in saidconditioning bath to thereby condition the exposed surfaces of saidfirst plastic component; activating said conditioned surface of saidfirst plastic component; applying an initial metallic coating to saidactivated surface in an electroless bath; finally processing saidjoined; multicomponent article in an electrolytic plating bath tothereby plate said exposed surfaces of said first component.
 9. A methodof making an article of manufacture comprising the following steps inthe order recited; joining a first plastic component consisting of anacrylonitrile butadiene styrene copolymer with a second plasticcomponent selected from the group consisting of polypropylene, apolysulfone, polyphenylene oxide, a polycarbonate, rigid polyvinylchloride and diallyl phthalate in a manner covering portions of thesurface of said first plastic component and leaving other portionsexposed thus selectively masking the surface of said first component;processing the joined multicomponent article in electroless platingbaths to thereby deposit an initial metallic coating on to the exposedsurfaces of said first plastic component; finally processing said joinedmulticomponent article in an electrolytic plating bath to therebyfurther plate said exposed metallic coated surface of said first plasticcomponent.